The present invention relates generally to a galvanic cell with a hermetically sealed cylindrical metal housing which is protected from the risk of explosion. The invention is applicable to primary electrochemical batteries as well as to storage batteries, insofar as they contain liquid electrolytes and are therefore at least sealed in a liquid-tight manner.
In connection with sealed, leak-proof housings, the potential exists for severe damage to the cell if it is used improperly or if it is subjected to extreme conditions, such as excessive charging, overheating, etc. As a consequence of these conditions, an abnormal internal gas or vapor pressure can develop which eventually causes leakage due to bursting of the cell housing.
Many of the known measures which are used in an effort to prevent such explosions are therefore based on pressure-sensitive devices. For example, according to DE-OS No. 3,206,607, a pointed screw is mounted over the lid of a hermetically sealed battery. The screw is capable of puncturing the lid when it is forced outwardly as a consequence of internal pressures developed in the battery, so that the contents of the battery may be squeezed out.
In GB-PS No. 1,336,567, a pressure relief valve for an alkaline cell is disclosed wherein a highly deformed cone made from an elastomer is press fit into a gas canal such that it ordinarily fills the canal, but so that it can be blown from the canal if extremely high pressures are encountered. In such case, the cone assumes another sealing position over the canal opening, but with a low degree of deformation which permits at least the overpressure to be released through a vent opening.
In DE-AS No. 26 20 466, a gas release valve is described wherein a seal comprised of a heat-sealable material fills a gas release opening which is provided in the wall of the cell, while adhering to a trough-shaped, recessed internal surface of the wall. If a sufficiently high internal pressure is reached, the material flows out through the pressure-relief opening in the wall, enabling the overpressure to escape from the interior of the battery.
Lastly, according to other prior art designs (e.g., GB-PS No. 1,445,043), the housing of the cell can be provided with a predetermined breaking point in order to protect the housing from bursting.
While cell explosions are extremely rare under ordinary operating conditions, the above-described cells are still susceptible to explosion when misused. This may include storage batteries which are exposed to fire either deliberately or through negligence, or primary cells which are subjected to charging, which is not permissible.